The present invention relates to a cutter arbor, having helicoidal cutters, for wood planing machines, which allows solving in a practical and economical manner the problem of the rational equipment of wood planing machines with cutting tools.
It is known that, at present, wood planing machines make use of a cutter arbor having rectilinear cutters, adjustable for regrinding, with the cutting edge parallel to the rotation axis of the arbor itself. Such cutters are fixed on the arbor with locking wedges and abutment screws in prismatic slots provided on the cutter arbor.
In the accompanying drawings, FIG. 1 is a perspective view of the arbor of a common wood planing machine, with a cutter inserted therein, while FIG. 2 is a cross-section of said arbor. These figures show the cutter arbor, a cutter, the lock wedge, the locking abutment screws, and the springs which facilitate the removal of the cutters when they have to be reground. In this construction, the cutters may be adjusted, provided that the cutting edges thereof are always kept on the same working diameter (a constructive and functional conception which has been widely adopted in the modern wood planing machines), and to allow the widest possible use of the cutters with regrinding, before their replacement.
With this arrangement, the regrinding can be carried out on the arbor itself through an appropriate grinder fitted on the planing machine, or else separately in the tool maintenance department of a workship. In the first case the grinding is usually more expensive, but more precise; in the second case the grinding is less expensive, but it is more difficult and it takes longer to lock the cutters on the arbor in such a precise position as to get all the cutting edges to work on the same diameter.
A cutter arbor as that heretofore described and illustrated in FIGS. 1 and 2 of the accompanying drawings, has the serious drawback of being quite noisy, both in the idle condition--because of the air being swirled by the cutters and hitting simultaneously, throughout the arbor length, the stationary surfaces close to the arbor (siren effect)--and, above all, during the cutting operation, when each single cutter hits the wooden board being planed throughout its width. This drawback--already widely felt in the field concerned--has lately become more serious due to the fact that, as is known, also for the machines involved, limits of upper sound level have been set by the international antipollution rules. The industries concerned have thus had to work out solutions to this problem.
Although many solutions have been proposed, only one of them has proved to solve the problem: the one adopting helicoidal cutting edges.
In this sense, two main lines have been followed: the first one provides for the use of rigid continuous helicoidal cutters, adjustable for regrinding and fixed to the arbor with the same system adopted for the rectilinear cutters, the lock wedges being also helicoidal; the second one adopts cutters in several portions, with the cutting edge parallel or slanting in respect of the arbor axis, arranged on the arbor itself in helicoidal sequence. This second solution is obtained with small cutters, which are adjustable for regrinding and fixed onto the cutter arbor either directly, or by axially connecting annular cutter-bearing elements, offset in a helicoidal direction, which carry small cutters of the type adjustable for regrinding, or else preground and not adjustable, to be thrown away when worn.
Neither of the two aforementioned solutions has however found practical use on a wide scale, for the followinng reasons.
Continuous helicoidal cutters:
They involve considerable costs in that, being rigid (cross sectional area of 3.div.4 mm.times.30.div.35 mm, as for rectilinear cutters), they have to be helicoidally shaped and, therefore, accurately machined to observe the helicoidal geometry.
They are difficult to adjust for regrinding in that, as the tool comes out, there is no longer any correspondence between the helicoidal geometry of the cutter and those of the wedge and of the prismatic slot of the arbor (the contacting surfaces as a result having different curvatures).
They must practically be reground on the cutter arbor with a very long operation, which is not easy as it has to be carried out under dry conditions and with special procedures, on account of the helicoidal shape.
Cutters in several portions:
They are easier to construct in that, even if positioned slanting in respect of the arbor axis, they are flat (on account of their limited length, the cutting angle varies only slightly), but their regrinding--whether carried out on the arbor, or out of it--is very long and toilsome, as can easily be appreciated.
The drawbacks of regrinding are overcome when pre-ground cutters are thrown away after wear, but in this case the overall cost becomes prohibitive, on account of the large number of cutters required for covering the whole arbor (order of magnitude: 40 cutters).